Active in Mexican dubbing since the 1960s, Najar originally played child or adolescent roles, notably the older Thumper in Bambi, Wart in The Sword in the Stone, and Rusty on the live-action series Rin Tin Tin.

Animation roles include Pepe LePew in Space Jam and Looney Tunes: Back in Action, Luigi in Cars, Inspector Gadget, Huckleberry Hound and Top Cat in various Hanna-Barbera specials, Fritz/Petunia in Meet the Robinsons, and Tony the Tiger in commercials.